Most electronic devices typically include a printed circuit board (PCB) to which a number of semiconductor components are mounted to perform a task in an application. In some applications, the electronic devices handle significant amounts of current that can produce enough heat within the device that the components or the PCB can be damaged unless the heat is dissipated. One such application arises from the use of inverters in electrical vehicles to control the conversion of DC battery power to three phase AC power for delivery to an electrical motor in the vehicle. The conversion of the DC current to AC current typically requires the use of metal oxide semiconductor field effect transistors (MOSFETs) mounted to the PCB. Sub-groups of the MOSFETs are driven by a controller to produce each of the phases in the AC current. The switching of these transistors to regulate the flow of the current through the transistors produces significant amounts of heat that need to be dissipated.
One solution to the problem of dissipating heat from semiconductors mounted to a PCB has been to use an insulated metal substrate (IMS). An IMS is composed of a metal sheet, such as aluminum, that is covered by a dielectric layer over which a circuit layer is laid. The metal substrate is usually mounted to a heat sink so the heat absorbed by the substrate from the circuit layer is removed from the metal substrate. The heat is conducted to the metal substrate through thermal vias formed as thermal conductive paths, such as copper, from an area of the circuit layer through the dielectric layer to the metal substrate. One drawback to this type of PCB is the outgassing of the solder paste that occurs when the semiconductor components are mounted to the PCB. This outgassing can form air pockets in the solder around the leads of the current conducting semiconductors and the air pockets degrade the ability of the semiconductors, such as MOSFETs, to conduct electrical current properly.
Another solution uses multi-layer PCBs. The multi-layer construction enabled some semiconductors to be mounted to one side of the PCB and other semiconductors to be mounted to the other side. This configuration is useful in some applications, but in applications where the current passing through the semiconductors can exceed 200 amps the thermal conductivity of the multi-layer PCB was deemed ineffective and device breakdown was more likely. Thus, finding a way of configuring a PCB and its semiconductor components in high current applications that produce significant amounts of heat without degrading the quality of the soldering of the components to the PCB would be beneficial.